Impact of Cation Multiplicity on Halide Perovskite Defect Densities and Solar Cell Voltages

• Published in: Journal of physical chemistry. C Vol. 124; no. 50; pp. 27333 - 27339
• Main Authors: Ledinský, Martin, Vlk, Aleš, Schönfeldová, Tereza, Holovský, Jakub, Aydin, Erkan, Dang, Hoang X, Hájková, Zdeňka, Landová, Lucie, Valenta, Jan, Fejfar, Antonín, De Wolf, Stefaan
• Format: Journal Article
• Language: English
• Published: American Chemical Society 17.12.2020
• Subjects: absorption; C: Energy Conversion and Storage; Energy and Charge Transport; cations; electric potential difference; iodides; lead; photoluminescence; solar cells
• ISSN: 1932-7447; 1932-7455; 1932-7455
• DOI: 10.1021/acs.jpcc.0c08193

Metal-halide perovskites feature very low deep-defect densities, thereby enabling high operating voltages at the solar cell level. Here, by precise extraction of their absorption spectra, we find that the low deep-defect density is unaffected when cations such as Cs+ and Rb+ are added during the perovskite synthesis. By comparing single crystals and polycrystalline thin films of methylammonium lead iodide/bromide, we find these defects to be predominantly localized at surfaces and grain boundaries. Furthermore, generally, for the most important photovoltaic materials, we demonstrate a strong correlation between their Urbach energy and open-circuit voltage deficiency at the solar cell level. Through external quantum yield photoluminescence efficiency measurements, we explain these results as a consequence of nonradiative open-circuit voltage losses in the solar cell. Finally, we define practical power conversion efficiency limits of solar cells by taking into account the Urbach energy.